As well known, electric cars are a type of energy-efficient and fast transportation, and have been gaining popularity among the general public. Electric cars are also a type of green transportation. As environmental awareness increases at various levels of the society, the usage of electric cars becomes more and more popular while the electric car industry has strong support from the community, including the government.
Battery is the “heart” of an electric car as the battery performance has a direct impact on the performance and quality of the electric car. Thus, an electric car's battery plays a very important role regarding the electric car. With respect to the battery itself, safety is a very important safety indicator.
The structure of a battery typically includes a safety valve disposed in the middle portion of an upper cover. Basic components of the safety valve include an aluminum gasket, a spring and a safety release. The safety release includes at least one orifice on its top side. The bottom side of the safety release (inside the casing of the battery) is connected with the aluminum gasket through the spring. During the manufacturing process of the battery, the battery is filled with a liquid electrolyte through an opening on the upper cover where the safety valve is located. After filling the battery with the liquid electrolyte, the aluminum gasket, the spring and the safety release are sequentially installed on the opening. When installed, the aluminum gasket and the spring seal up the opening. Under normal operating conditions, there is no gas inside the battery casing. Further, external gas and moisture cannot enter into the battery due to the spring-loaded aluminum gasket. When gas forms inside the battery as a result of electrolysis, the spring is compressed under pressure and protrudes upwardly, as the spring has a certain elastic modulus, and moves the aluminum gasket upwardly. A certain ventilation gap is formed as a result of the movement of the aluminum gasket, thus allowing the internal gas to pass through the gap and be ventilated out of the battery through the orifice of the safety release.
There are a number of issues associated with the above-described safety valve structure. Firstly, as the spring and the aluminum gasket age after a long period of operation, external gas and moisture can easily enter into the battery. The aging of the spring and the aluminum gasket may also result in the internally-formed gas not being timely ventilated out of the battery. This results in increased internal pressure that may cause the battery casing to rupture. Undesirably there is a risk of explosion of the battery at such time. Secondly, externally-installed safety valves of this type tend to have complex structure that require more complex process, time and cost for manufacturing.